Theory of the Orphan Planet

Mother Nature Network has an intriguing article about David Nesvorny from Colorado’s Southwest Research Institute, who did a mathematical analysis of the formation of our solar system. After running 6,000 computer simulations, he reached the conclusion that a fifth gas giant prevented Jupiter, Saturn, Uranus, and Neptune from destroying one another, then was hurtled into space by Jupiter's gravitational field, joining other free-floating planets in interstellar space.